Manufacture of metal strip from metal powder



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I MANUFACTURE OF METAL STRIP FROM METAL POWDER Filed July 18, 1956 2Sheets-Sheet 2 camwcrwva r0 8779/1 an 054F517 52142? FEZIQW/AZ) SIV/QIAO/fl/YAV'EF 170118 FIRST STAGE 0040 Fall/4'6 AVA/41 P600067 V607 779/41Alla/{4 STE/P arr-0194 5;

2,889,224 lag Patented June 2, 1959 MANUFACTURE OF METAL STRIP FROM WTALPOWDER v 7 Application July 18, 1956, Serial No. 598,693

Claims priority, application Great Britain 7 July 20, 1955 2 Claims.(Cl. 75-214) The present invention relates to a method for producingsintered metal strip and more particularly to a method for producingthin metal strip by direct rolling of metal powder and especially to themanufacture of thin strip material of nickel or of iron or of both bythe direct rolling of the metal powder.

It is well known that metal strip can be made frorn metal powder bypassing the powder between rolls arranged so as to compress the powderinto a continuous compact and thereafter sintering the compact. It. hasbeen proposed to make metal strip from nickel powder produced by thethermal decomposition of nickel carbonyl. It is known that when nickelis thermally decomposed to yield the corresponding metal powder the kindof powder produced depends upon the operating 7 conditions in thedecomposen Normally the powder is in the form of discrete particles, butif the throughput of the carbonyl or the heat input of the decomposer orboth is or are increased the powder particles agglomerate and thestructure of the product becomes fibrous, the bulk density of the powderbeing much less than that of the other kind of powder. These two powdersare often known, as A type and B type, respectively. The A type metalpowders have relatively free flowing discrete particles which do notreadily combine together under compression. Although the interlockingaggregate structure of the B type powder particles enables them to mattetogether when the powder is compacted, this type of powder has poor flowproperties. Powder consisting wholly or mainly of discrete particles andwhich will now be referred to as A powder has a bulk density of between2 to 2.6 grams per cubic centimetre whereas powder wholly or mainly withthe fibrous structure, which will now be referred to as B powder, has abulk density of between 0.6 to 1.4 grams per cubic centimetre. It hasbeen found that when compacting rolls are used of a large enoughdiameter to allow adequate feed of B 7 type powder into the roll gap,for example, 8 inch diameter rolls, the relatively thick strip thusproduced by the compacting rolls has excellent strength and resilienceto withstand the mechanical stress of handling before and during itspassage through the sintering furnace. However, when attempts have beenmade to produce a thin compact of about 0.005 inch thickness or even0.01 inch thickness from the B type powder using smaller diametercompacting rolls 'such as about 2% inches diameter, difficulties aroseand adequate feed of the B -type powder into the roll gap was notobtainable, the

strip produced being of non-uniform density. Although attempts were madeto overcome the foregoing difiiculties by, e.g., roughening the rolls,none was entirely suc cessful when carried into practice commercially onan inmetal powder between rolls arranged to compress the powder into acontinuous compact and thereafter sintering the compact, may beexpeditiously and economically formed from a special mixture of twokinds of the particular carbonyl-metal whereby the strength of the stripof compacted material before sintering is greater than that of a stripformed of the A type powder alone.

It is an object of the present invention to provide an improved methodfor producing thin metal strip of compacted nickel-carbonyl powder, ofiron carbonyl powder, or of both and having high strength beforesintering.

Another object of the invention is to provide an improved method forproducing thin metal strip from nickelcarbonyl powder, from ironcarbonyl powder, and from both.

The invention also contemplates providing an improved method forproducing thin metal strip from nickel-carbonyl powder, wherein thestrength of the compacted metal strip before sintering is greater thanthat of a strip formed of the corresponding A type metal powder alone.

It is a further object of the invention to provide an improved thinmetal strip made from nickel-carbonyl powder, wherein the strength ofthe compacted metal strip before sintering is greater than that of astrip formed of the corresponding A type metal powder alone.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawing in which:

Figure 1 is a graphical representation showing the relation between thecompacting roll diameter and the thickness of the strip beforesintering; and

Figure 2 depicts a flow sheet of an embodiment of the invention.

Generally speaking, the present invention relates to an improved processfor preparing thin metal strip comprising compacting and sinteringcarbonyl-nickel powder. The improved results of the invention areachieved when a special mixture of the B type powder and of the A typepowder of the particular carbonyl-metal used is compacted between rollsinto strip form. The mixture of these metal powders used according tothe invention contains from about 25% to 95% A type powder by weight,the remainder being B type powder. For example, when preparing thinnickel strip from carbonyl nickel powders the mixture of these powdersshould contain from about 5% to about B type powder by weight. The stripis then compacted between relatively small diameter rolls say not lessthan 2 inches diameter up to about 4 inches diameter with a nominal gapwidth of 0.005 inch. The compacted strip is between 0.004

and 0.010 inch thick. In a mass of powder fed to the rolls there is acompacting zone above the bite of the said rolls and if it is shallow asis the case with small rolls, the powder tends to bridge over and notenter the bite but with a mixture as quoted above this problem isobviated. The compacted strip issues from the bite and passes into asintering furnace and is subjected to a temthickness is effected inrolls of very small diameter say approximately'Vs inch. 7 I V Theproportion of Bftype powder in the mixture of carbonyl-metal powdersaffects the thickness of the compacted strip produced with a given gapsetting, that is to say the distance apart of the compacting rolls, the

3 strength of the strip and the appearance of the strip. There is anoptimum gap setting of the compacting rolls which depends on the rolldiameter. For example, when using compacting rolls about 2% inches indiameter the nominal gap setting should not exceed about 0.007 inch.With these rolls the maximum strength is obtained when the proportion ofB type carbonyl-nickel power is about 70% (30% A). At a proportion ashigh as this, however, the strip is distinctly mottled in appearance,indicating lack of uniformity which is itself the result of thecomparatively poor flowing properties of the B type powder. It ispreferred not to use the proportion of B type carbonyl-metal powder thatprovides maximum strength in the compacting strip, but rather to keepthe B type. powder at not more than about 50% of the mixture, forexample, not more than about 50% of B type carbonyl-nickel powder whenmaking nickel strip.

For a given setting of the roll gap and roll diameter, no more A typecarbonyl-metal powder should be added than is sufficient to ensureadequate feed of the poW- der between the rolls, since further additionsof A type powder progressively reduce the strength of the compact edstrip before sintering.

It is more economical to produce very thin strip from a thin striprather than a relatively thick one, for then the amount of subsequentworking is much reduced. For example, it would be a decided advantage inthe case of very thin strip of about 0.001 inch thickness to producethis with some working from a strip of say 0.005 inch thickness onrelatively small diameter rolls rather than make it from strip of 0.020inch made on relatively large diameter rolls. There is a direct relationbetween roll diameter and the thickness of strip which can be producedby direct rolling. This relationship is shown by the graph in Figure 1of the drawing.

For the purpose of giving those skilled in the art a. betterunderstanding of the invention, the following illustrative example isgiven:

A very thin metal strip was produced by the novel method of thisinvention as outlined in the flow sheet depicted in Figure 2 of thedrawing. This very thin metal strip was formed from a powder mixtureconsisting of 50% A type carbonyl-nickel powder and 50% B typecarbonyl-nickel powder. The A type powder was of approximately 4 micronparticle size as determined by the gas-permeability method and had abulk density of 2.6 grams per cubic centimetre. The B type powder was ofapproximately 3 micron particle size and had a bulk density of 0.9 gramper cubic centimetre. The mixture of carbonyl-nickel powders wascompacted between rolls 2% inches in diameter to form a continuous strip0.006 inch thick and 2 inches wide at a speed of feet per minute. Thestrip of compacted material then was passed directly through a tubefurnace having a hot zone 2 feet long maintained at a temperature of 900C. to 1200 C. The protective atmosphere in the tube furnace washydrogen. However, cracked ammonia may be used as the atmosphere in thefurnace. The sintered strip leaving the furnace was found to be ductile.The sintered strip was cold-rolled in four or five stages withintermediate annealing treatments, each carried out by passage of thestrip at a speed of 10 feet per minute through a furnace having a hotzone 2 feet long maintained at a temperature of 900 C. to 1200 C. in aprotective atmosphere. The total reduction in thickness of the strip was70%. The finished strip possessed a well-developed crystal structure andwas free from porosity.

Although the invention has been described in detail with respect to theproduction of thin metal strip from carbonyl-nickel powder, similarconsiderations apply in the case of thin strip prepared fromcarbonyl-iron powder.

It will be appreciated that the invention has wide applicability. Forillustrative purposes, it is noted that the present invention isparticularly applicable to powders of high and low bulk density. It isgenerally accepted that bulk density is a convenient criterion of theflow characteristic of a powder in that it is indicative of the surfacestructure of the particles comprising the powder. A low bulk densitypowder has a poor flow characteristic and it is possible to enhance theflow by adding a proportion of a powder of a higher bulk density. It hasbeen found that powder other than carbonyl powder of low bulk densitymay be compacted with small rolls to give a strip of good green strengthif a proportion of higher bulk density powder is added to enhance theflow. For example, electrolytic or hydrogen reduced copper powders havepoor flow characteristics and good bonding properties and the flow canbe enhanced using small rolls by adding a proportion of atomized copperpowder which has a spherical particle and good flow characteristic.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. The method for producing by direct rolling a substantially non-porousthin metal strip from carbonyl nickel powder which comprisesestablishing a mixture containing about 5% to by weight of a carbonylnickel powder having a bulk density between about 0.6 and 1.4 grams percubic centimeter and characterized by a fibrous structure and poor flowproperties and about to 25% by weight of a carbonyl nickel powder havinga bulk density between about 2 and 2.6 grams per cubic centimeter andcharacterized by being in the form of discrete particles; passing saidmixture of carbonyl nickel powder through compacting rolls having adiameter between about 2 inches and about 4 inches to produce acompacted metal strip of uniform structure and having a thickness ofabout 0.004 inch to 0.010 inch, said compacted strip having a greaterstrength than a similar strip made only from said carbonyl nickel powderhaving discrete particles and having greater uniformity than a similarstrip made only from said nickel powder having a fibrous structure;sintering said compacted strip and reducing said sintered compactedstrip to a ductile nonporous form by cold rolling and annealing.

2. The method for producing by direct rolling a substantially non-porousthin metal strip from carbonyl nickel powder which comprisesestablishing a mixture containing about 50% by weight of a carbonylnickel powder having a particle size of approximately 4 microns and a'bulk density of 2.6 grams per cubic centimeter and about 50% by Weightof a carbonyl nickel powder having a particle size of approximately 3microns and a bulk density of 0.9 gram per cubic cenitmeter; compactingsaid mixture of carbonyl nickel powder between rolls of about 2% inchesdiameter to form a continuous strip about 0.006 inch thick; sinteringsaid compacted strip and thereafter reducing said sintered compactedstrip to a non-porous nickel strip by cold rolling and annealing.

References Cited in the file of this patent UNITED STATES PATENTS2,337,588 Calkins Dec. 28, 1943 2,341,732 Marvin Feb. 15, 1944 2,758,336Franssen Aug. 14, 1956 2,771,637 Si1vasy et al Nov. 27, 1956 FOREIGNPATENTS 311,141 Great Britain July 9, 1928 in -...x

1. THE METHOD FOR PRODUCING BY DIRECT ROLLING A SUBSTANTIALLY NON-POROUSTHIN METAL STRIP FROM CARBONYL NICKEL POWDER WHICH COMPRISESESTABLISHING A MIXTURE CONTAINING ABOUT 5% TO 75% BY WEIGHT OF ACARBONYL NICKEL POWDER HAVING A BULK DENSITY BETWEEN ABOUT 0.6 AND 1.4GRAMS PER CUBIC CENTIMETER AND CHARACTERIZED BY A FIBROUS STRUCTURE ANDPOOR FLOW PROPERTIES AND ABOUT 95% TO 25% BY WEIGHT OF A CARBONYL NICKELPOWDER HAVING A BULK DENSITY BETWEEN ABOUT 2 AND 2.6 GRAMS PER CUBICCENTIMERTER AND CHARACTERIZED BY BEING IN THE FORM OF DISCRETEPARTICLES; PASSING SAID MIXTURE OF CARBONYL NICKEL POWDER THROUGHCOMPACTING ROLLS HAVING A DIAMETER BETWEEN ABOUT 2 INCHES AND ABOUT 4INCHES TO PRODUCE A COMPACTED METAL STRIP OF UNIFORM STRUCTURE ANDHAVING A THICKNESS OF ABOUT 0.004 INCH TO 0.010 INCH, SAID COM-